examples/tools/contiguouscache/randomlistmodel.cpp
author Dremov Kirill (Nokia-D-MSW/Tampere) <kirill.dremov@nokia.com>
Tue, 02 Feb 2010 00:43:10 +0200
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permissions -rw-r--r--
Revision: 201003 Kit: 201005
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/****************************************************************************
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**
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** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
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** All rights reserved.
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** Contact: Nokia Corporation (qt-info@nokia.com)
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**
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** This file is part of the examples of the Qt Toolkit.
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**
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** $QT_BEGIN_LICENSE:LGPL$
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** No Commercial Usage
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** This file contains pre-release code and may not be distributed.
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** You may use this file in accordance with the terms and conditions
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** contained in the Technology Preview License Agreement accompanying
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** this package.
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**
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** GNU Lesser General Public License Usage
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** Alternatively, this file may be used under the terms of the GNU Lesser
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** General Public License version 2.1 as published by the Free Software
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** Foundation and appearing in the file LICENSE.LGPL included in the
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** packaging of this file.  Please review the following information to
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** ensure the GNU Lesser General Public License version 2.1 requirements
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** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
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**
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** In addition, as a special exception, Nokia gives you certain additional
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** rights.  These rights are described in the Nokia Qt LGPL Exception
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** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
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**
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** If you have questions regarding the use of this file, please contact
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** Nokia at qt-info@nokia.com.
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**
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**
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**
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**
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**
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**
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**
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**
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** $QT_END_LICENSE$
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**
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****************************************************************************/
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#include "randomlistmodel.h"
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#include <stdlib.h>
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static const int bufferSize(500);
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static const int lookAhead(100);
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static const int halfLookAhead(lookAhead/2);
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RandomListModel::RandomListModel(QObject *parent)
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: QAbstractListModel(parent), m_rows(bufferSize), m_count(10000)
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{
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}
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RandomListModel::~RandomListModel()
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{
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}
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int RandomListModel::rowCount(const QModelIndex &) const
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{
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    return m_count;
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}
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//! [0]
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QVariant RandomListModel::data(const QModelIndex &index, int role) const
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{
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    if (role != Qt::DisplayRole)
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        return QVariant();
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    int row = index.row();
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    if (row > m_rows.lastIndex()) {
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        if (row - m_rows.lastIndex() > lookAhead)
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            cacheRows(row-halfLookAhead, qMin(m_count, row+halfLookAhead));
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        else while (row > m_rows.lastIndex())
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            m_rows.append(fetchRow(m_rows.lastIndex()+1));
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    } else if (row < m_rows.firstIndex()) {
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        if (m_rows.firstIndex() - row > lookAhead)
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            cacheRows(qMax(0, row-halfLookAhead), row+halfLookAhead);
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        else while (row < m_rows.firstIndex())
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            m_rows.prepend(fetchRow(m_rows.firstIndex()-1));
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    }
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    return m_rows.at(row);
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}
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void RandomListModel::cacheRows(int from, int to) const
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{
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    for (int i = from; i <= to; ++i)
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        m_rows.insert(i, fetchRow(i));
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}
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//![0]
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//![1]
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QString RandomListModel::fetchRow(int position) const
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{
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    return QString::number(rand() % ++position);
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}
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//![1]